As a commonly-used function of a display panel, a brightness control function is used to control a brightness value of a display panel. For a conventional liquid crystal display (LCD) panel, a voltage output mode for pulse width modulation (PWM) is adjusted by a light-emission diode (LED)-driver integrated circuit (IC), so as to control the brightness value of a backlight source, thereby to control the brightness of the LCD panel. However, some display panels, e.g., AMOLED panels, are not provided any backlight modules. For the AMOLED panel, a metal-oxide semiconductor (MOS) transistor is energized by a potential difference between a positive power supply voltage ELVDD and a negative power supply voltage ELVSS generated by a power IC, so as to generate a current to drive an OLED to emit light. A source IC outputs a data signal, and a driving thin film transistor (TFT) cooperates with a switching TFT so as to perform pixel display control. Currently, it is impossible to adjust the brightness of the AMOLED panel in a 256-grayscale (which also may be referred to gamma-level since the grayscale is adjusted by adjusting the gamma voltage) manner.